1. Field of the Invention
The present invention relates generally to clock transmission and recovery.
2. Background Art
Embedding a clock signal in a transmitted data stream is a known method for transmitting a clock signal from a transmitter to a receiver in applications requiring clock synchronization between the transmitter and the receiver. One problem associated with this method is the electromagnetic interference (EMI) caused by transmitting the clock signal in the data stream. Specifically, embedding the clock signal into the data stream causes additional EMI components at harmonic frequencies of the clock frequency to be imposed over the broadband EMI spectrum due to the data transmitted.
One technique for reducing EMI due to clock signal transmission uses spread spectrum (SS) modulation to spread EMI components due to the clock over frequency. However, the SS modulation technique causes jitter in the transmitted clock in the time domain. For this reason, the SS modulation technique for reducing EMI cannot be used in systems that require tight clock synchronization between the transmitter and the receiver, such as in high-speed communication networks (and especially networks which use echo cancellation between transceivers), for example.
The present invention will be described with reference to the accompanying drawings. Generally, the drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.